Substrate holder, lithographic apparatus, device manufacturing method, and method of manufacturing a substrate holder

ABSTRACT

A substrate holder for a lithographic apparatus has a main body having a thin-film stack provided on a surface thereof. The thin-film stack forms an electronic or electric component such as an electrode, a sensor, a heater, a transistor or a logic device, and has a top isolation layer. A plurality of burls to support a substrate are formed on the thin-film stack or in apertures of the thin-film stack.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. provisional application61/594,857, which was filed on Feb. 3, 2012, U.S. provisionalapplication 61/621,648, which was filed on Apr. 9, 2012 and U.S.provisional application 61/621,660, which was filed on Apr. 9, 2012 andwhich are incorporated herein in its entirety by reference.

FIELD

The present invention relates to a substrate holder, a lithographicapparatus, a device manufacturing method, and a method of manufacturinga substrate holder.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits (ICs). In that instance, a patterning device, whichis alternatively referred to as a mask or a reticle, may be used togenerate a circuit pattern to be formed on an individual layer of theIC. This pattern can be transferred onto a target portion (e.g.comprising part of, one, or several dies) on a substrate (e.g. a siliconwafer). Transfer of the pattern is typically via imaging onto a layer ofradiation-sensitive material (resist) provided on the substrate. Ingeneral, a single substrate will contain a network of adjacent targetportions that are successively patterned. Known lithographic apparatusinclude so-called steppers, in which each target portion is irradiatedby exposing an entire pattern onto the target portion at one time, andso-called scanners, in which each target portion is irradiated byscanning the pattern through a radiation beam in a given direction (the“scanning”-direction) while synchronously scanning the substrateparallel or anti-parallel to this direction. It is also possible totransfer the pattern from the patterning device to the substrate byimprinting the pattern onto the substrate.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in a liquid having a relatively high refractiveindex, e.g. water, so as to fill a space between the final element ofthe projection system and the substrate. In an embodiment, the liquid isdistilled water, although another liquid can be used. An embodiment ofthe present invention will be described with reference to liquid.However, another fluid may be suitable, particularly a wetting fluid, anincompressible fluid and/or a fluid with higher refractive index thanair, desirably a higher refractive index than water. Fluids excludinggases are particularly desirable. The point of this is to enable imagingof smaller features since the exposure radiation will have a shorterwavelength in the liquid. (The effect of the liquid may also be regardedas increasing the effective numerical aperture (NA) of the system andalso increasing the depth of focus.) Other immersion liquids have beenproposed, including water with solid particles (e.g. quartz) suspendedtherein, or a liquid with a nano-particle suspension (e.g. particleswith a maximum dimension of up to 10 nm). The suspended particles may ormay not have a similar or the same refractive index as the liquid inwhich they are suspended. Other liquids which may be suitable include ahydrocarbon, such as an aromatic, a fluorohydrocarbon, and/or an aqueoussolution.

SUMMARY

In a conventional lithography apparatus, the substrate to be exposed maybe supported by a substrate holder which in turn is supported by asubstrate table. The substrate holder is often a flat rigid disccorresponding in size and shape to the substrate (although it may have adifferent size or shape). It has an array of projections, referred to asburs or pimples, projecting from at least one side. In an embodiment,the substrate holder has an array of projections on two opposite sides.In this case, when the substrate holder is placed on the substratetable, the main body of the substrate holder is held a small distanceabove the substrate table while the ends of the buds on one side of thesubstrate holder lie on the surface of the substrate table. Similarly,when the substrate rests on the top of the burls on the opposite side ofthe substrate holder, the substrate is spaced apart from the main bodyof the substrate holder. One purpose of this is to help prevent aparticle (i.e. a contaminating particle such as a dust particle) whichmight be present on either the substrate table or substrate holder fromdistorting the substrate holder or the substrate. Since the totalsurface area of the burs is only a small fraction of the total area ofthe substrate or substrate holder, it is highly probable that anyparticle will lie between burls and its presence will have no effect.

Due to the high accelerations experienced by the substrate in use of ahigh-throughput lithographic apparatus, it is not sufficient to allowthe substrate simply to rest on the burls of the substrate holder. It isclamped in place. Two methods of clamping the substrate in place areknown—vacuum clamping and electrostatic clamping. In vacuum clamping,the space between the substrate holder and substrate and optionallybetween the substrate table and substrate holder are partially evacuatedso that the substrate is held in place by the higher pressure of gas orliquid above it. Vacuum clamping however may not be feasible where thebeam path and/or the environment near the substrate or substrate holderis kept at a low or very low pressure, e.g. for extreme ultraviolet(EUV) radiation lithography. In this case, it may not be possible todevelop a sufficiently large pressure difference across the substrate(or substrate holder) to clamp it. Electrostatic clamping can thereforebe used in such a circumstance (or in other circumstances). Inelectrostatic clamping, an electrode provided on the substrate tableand/or substrate holder is raised to a high potential, e.g. 10 to 5000V, and electrostatic forces attract the substrate. Thus another purposeof the burls is to space the substrate, substrate holder and substratetable apart in order to enable electrostatic clamping.

Temperature control over the substrate surface is significant, inparticular in immersion systems which are sensitive to temperaturevariations due to liquid (e.g. water) evaporation effects. Evaporationof liquid removes heat from the substrate, causing temperaturevariations. These temperature variations may lead to thermal stress inthe substrate which eventually may contribute to overlay error. Toimprove accuracy of temperature control, real time local measurement ofthe temperature combined with active heating is desired. Such ameasurement and heating system is integrated into the system, e.g. inthe substrate holder (i.e. the object that directly supports asubstrate) and/or substrate table (mirror block of stage, i.e. theobject that supports the substrate holder and provides the upper surfacesurrounding the substrate holder). A thin-film stack can be used to makea structure that can both measure and heat such a structure and offersthe opportunity for integration into the substrate holder and/or table.

It is desirable, for example, to provide a substrate table or substrateholder on which one or more electronic or electric components, such asone or more thin-film components, are formed.

According to an aspect of the invention, there is provided a substrateholder for use in a lithographic apparatus, the substrate holdercomprising: a main body having a surface; a thin-film stack provided onthe surface and forming an electronic or electric component; and aplurality of burls provided on the thin-film stack and having endsurfaces to support a substrate.

According to an aspect of the present invention, there is provided alithographic apparatus, comprising: a support structure configured tosupport a patterning device; a projection system arranged to project abeam patterned by the patterning device onto a substrate; and asubstrate holder arranged to hold the substrate, the substrate holderbeing as described herein.

According to an aspect of the present invention, there is provided adevice manufacturing method using a lithographic apparatus, the methodcomprising: projecting a beam patterned by a patterning device onto asubstrate while holding the substrate in a substrate holder, wherein thesubstrate holder comprises: a main body having a surface; a thin-filmstack provided on the surface and forming an electronic or electriccomponent; and a plurality of burs provided on the thin-film stack andhaving end surfaces to support a substrate.

According to an aspect of the present invention, there is provided amethod of manufacturing a substrate holder for use in a lithographicapparatus, the method comprising: providing a main body having asurface; forming a thin-film stack on the surface of the main body; andforming a plurality of burls on the thin-film stack projecting from thesurface and having end surfaces to support a substrate.

According to an aspect of the present invention, there is provided amethod of manufacturing a substrate holder for use in a lithographicapparatus, the method comprising: providing a main body having asurface; forming a thin-film stack on the surface of the main body;forming a plurality of apertures in the thin-film stack; and forming aplurality of burs in the apertures of the thin-film stack, the bursprojecting from the stack and having end surfaces to support asubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIGS. 2 and 3 depict a liquid supply system for use in a lithographicprojection apparatus;

FIG. 4 depicts a further liquid supply system for use in a lithographicprojection apparatus;

FIG. 5 depicts, in cross-section, a barrier member which may be used inan embodiment of the present invention as an immersion liquid supplysystem;

FIG. 6 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 7 is a more detailed view of the apparatus 4100;

FIG. 8 is a more detailed view of the source collector apparatus SO ofthe apparatus of FIGS. 6 and 7 ;

FIG. 9 depicts in cross-section a substrate table and a substrate holderaccording to an embodiment of the invention;

FIG. 10 depicts steps in a method of manufacturing a substrate holderaccording to an embodiment of the invention;

FIG. 11 depicts steps in a method of manufacturing a substrate holderaccording to an embodiment of the invention;

FIG. 12 depicts steps in a method of manufacturing a substrate holderaccording to an embodiment of the invention;

FIGS. 13 to 15 depict thin-film stacks according to embodiments of theinvention;

FIG. 16 depicts schematically an electrostatic clamp arrangementaccording to an embodiment of the invention;

FIG. 17 depicts schematically another electrostatic clamp arrangementaccording to an embodiment of the invention;

FIG. 18 depicts steps in a method of manufacturing a substrate holderaccording to an embodiment of the invention;

FIGS. 19A to 19E depict steps in a method of manufacturing a substrateholder according to an embodiment of the invention; and

FIG. 20 depicts a substrate holder according to an embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to oneembodiment of the invention. The apparatus comprises:

-   -   an illumination system (illuminator) IL configured to condition        a radiation beam B (e.g. UV radiation, DUV radiation or EUV        radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask) MA and connected to a        first positioner PM configured to accurately position the        patterning device in accordance with certain parameters;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate in accordance with certain parameters; and    -   a projection system (e.g. a refractive projection lens system)        PS configured to project a pattern imparted to the radiation        beam B by patterning device MA onto a target portion C (e.g.        comprising one or more dies) of the substrate W.

The illumination system may include various types of optical components,such as refractive, reflective, magnetic, electromagnetic, electrostaticor other types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT holds the patterning device. The supportstructure MT holds the patterning device in a manner that depends on theorientation of the patterning device, the design of the lithographicapparatus, and other conditions, such as for example whether or not thepatterning device is held in a vacuum environment. The support structureMT can use mechanical, vacuum, electrostatic or other clampingtechniques to hold the patterning device. The support structure MT maybe a frame or a table, for example, which may be fixed or movable asrequired. The support structure MT may ensure that the patterning deviceis at a desired position, for example with respect to the projectionsystem. Any use of the terms “reticle” or “mask” herein may beconsidered synonymous with the more general term “patterning device”.

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a radiation beamwith a pattern in its cross-section such as to create a pattern in atarget portion of the substrate. It should be noted that the patternimparted to the radiation beam may not exactly correspond to the desiredpattern in the target portion of the substrate, for example if thepattern includes phase-shifting features or so called assist features.Generally, the pattern imparted to the radiation beam will correspond toa particular functional layer in a device being created in the targetportion, such as an integrated circuit.

The patterning device may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam in different directions. The tilted mirrorsimpart a pattern in a radiation beam which is reflected by the mirrormatrix.

The terms “projection system” used herein should be broadly interpretedas encompassing any type of system, including refractive, reflective,catadioptric, magnetic, electromagnetic and electrostatic opticalsystems, or any combination thereof, as appropriate for the exposureradiation being used, or for other factors such as the use of animmersion liquid or the use of a vacuum. Any use of the term “projectionlens” herein may be considered as synonymous with the more general term“projection system”.

As here depicted, the apparatus is of a transmissive type (e.g.employing a transmissive mask). Alternatively, the apparatus may be of areflective type (e.g. employing a programmable mirror array of a type asreferred to above, or employing a reflective mask).

The lithographic apparatus may be of a type having two or more substratesupport structures, such as substrate stages or substrate tables, and/ortwo or more support structures for patterning devices. In an apparatuswith multiple substrate stages, all the substrate stages can beequivalent and interchangeable. In an embodiment, at least one of themultiple substrate stages is particularly adapted for exposure steps andat least one of the multiple substrate stages is particularly adaptedfor measurement or preparatory steps. In an embodiment of the inventionone or more of the multiple substrate stages is replaced by ameasurement stage. A measurement stage includes at least part one ormore sensor systems such as a sensor detector and/or target of thesensor system but does not support a substrate. The measurement stage ispositionable in the projection beam in place of a substrate stage or asupport structure for a patterning device. In such apparatus theadditional stages may be used in parallel, or preparatory steps may becarried out on one or more stages while one or more other stages arebeing used for exposure.

Referring to FIG. 1 , the illuminator IL receives a radiation beam froma radiation source SO. The source and the lithographic apparatus may beseparate entities, for example when the source is an excimer laser. Insuch cases, the source is not considered to form part of thelithographic apparatus and the radiation beam is passed from the sourceSO to the illuminator IL with the aid of a beam delivery system BDcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thelithographic apparatus, for example when the source is a mercury lamp.The source SO and the illuminator IL, together with the beam deliverysystem BD if required, may be referred to as a radiation system.

The illuminator IL may comprise an adjuster AM configured to adjust theangular intensity distribution of the radiation beam. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator may be used tocondition the radiation beam, to have a desired uniformity and intensitydistribution in its cross-section. Similar to the source SO, theilluminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The radiation beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. Having traversed the patterningdevice MA, the radiation beam B passes through the projection system PS,which focuses the beam onto a target portion C of the substrate W.Substrate W is held on the substrate table WT by a substrate holderaccording to an embodiment of the present invention and describedfurther below. With the aid of the second positioner PW and positionsensor IF (e.g. an interferometric device, linear encoder or capacitivesensor), the substrate table WT can be moved accurately, e.g. so as toposition different target portions C in the path of the radiation beamB. Similarly, the first positioner PM and another position sensor (whichis not explicitly depicted in FIG. 1 ) can be used to accuratelyposition the patterning device MA with respect to the path of theradiation beam B, e.g. after mechanical retrieval from a mask library,or during a scan. In general, movement of the support structure MT maybe realized with the aid of a long-stroke module (coarse positioning)and a short-stroke module (fine positioning), which form part of thefirst positioner PM. Similarly, movement of the substrate table WT maybe realized using a long-stroke module and a short-stroke module, whichform part of the second positioner PW. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed. Patterning device MA andsubstrate W may be aligned using patterning device alignment marks M1,M2 and substrate alignment marks P1, P2. Although the substratealignment marks as illustrated occupy dedicated target portions, theymay be located in spaces between target portions (these are known asscribe-lane alignment marks). Similarly, in situations in which morethan one die is provided on the patterning device MA, the patterningdevice alignment marks may be located between the dies.

The depicted apparatus could be used in at least one of the followingmodes:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theradiation beam is projected onto a target portion C at one time (i.e. asingle static exposure). The substrate table WT is then shifted in the Xand/or Y direction so that a different target portion C can be exposed.In step mode, the maximum size of the exposure field limits the size ofthe target portion C imaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the radiation beam isprojected onto a target portion C (i.e. a single dynamic exposure). Thevelocity and direction of the substrate table WT relative to the supportstructure MT may be determined by the (de-)magnification and imagereversal characteristics of the projection system PS. In scan mode, themaximum size of the exposure field limits the width (in the non-scanningdirection) of the target portion in a single dynamic exposure, whereasthe length of the scanning motion determines the height (in the scanningdirection) of the target portion.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the radiationbeam is projected onto a target portion C. In this mode, generally apulsed radiation source is employed and the programmable patterningdevice is updated as required after each movement of the substrate tableWT or in between successive radiation pulses during a scan. This mode ofoperation can be readily applied to maskless lithography that utilizesprogrammable patterning device, such as a programmable mirror array of atype as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

In many lithographic apparatuses, a fluid, in particular a liquid, isprovided between the final element of the projection system using aliquid supply system IH to enable imaging of smaller features and/orincrease the effective NA of the apparatus. An embodiment of theinvention is described further below with reference to such an immersionapparatus, but may equally be embodied in a non-immersion apparatus.Arrangements to provide liquid between a final element of the projectionsystem and the substrate can be classed into at least two generalcategories. These are the bath type arrangement and the so calledlocalized immersion system. In the bath type arrangement substantiallythe whole of the substrate and optionally part of the substrate table issubmersed in a bath of liquid. The localized immersion system uses aliquid supply system in which liquid is only provided to a localizedarea of the substrate. In the latter category, the space filled byliquid is smaller in plan than the top surface of the substrate and thearea filled with liquid remains substantially stationary relative to theprojection system while the substrate moves underneath that area.Another arrangement, to which an embodiment of the invention isdirected, is the all wet solution in which the liquid is unconfined. Inthis arrangement substantially the whole top surface of the substrateand all or part of the substrate table is covered in immersion liquid.The depth of the liquid covering at least the substrate is small. Theliquid may be a film, such as a thin-film, of liquid on the substrate.

Four different types of localized liquid supply systems are illustratedin FIGS. 2 to 5 . Any of the liquid supply devices of FIGS. 2 to 5 maybe used in an unconfined system; however, sealing features are notpresent, are not activated, are not as efficient as normal or areotherwise ineffective to seal liquid to only the localized area.

One of the arrangements proposed for a localized immersion system is fora liquid supply system to provide liquid on only a localized area of thesubstrate and in between the final element of the projection system andthe substrate using a liquid confinement system (the substrate generallyhas a larger surface area than the final element of the projectionsystem). One way which has been proposed to arrange for this isdisclosed in PCT patent application publication no. WO 99/49504. Asillustrated in FIGS. 2 and 3 , liquid is supplied by at least one inletonto the substrate, desirably along the direction of movement of thesubstrate relative to the final element, and is removed by at least oneoutlet after having passed under the projection system. That is, as thesubstrate is scanned beneath the element in a −X direction, liquid issupplied at the +X side of the element and taken up at the −X side.

FIG. 2 shows the arrangement schematically in which liquid is suppliedvia inlet and is taken up on the other side of the element by outletwhich is connected to a low pressure source. The arrows above thesubstrate W illustrate the direction of liquid flow, and the arrow belowthe substrate W illustrates the direction of movement of the substratetable. In the illustration of FIG. 2 the liquid is supplied along thedirection of movement of the substrate relative to the final element,though this does not need to be the case. Various orientations andnumbers of in- and out-lets positioned around the final element arepossible, one example is illustrated in FIG. 3 in which four sets of aninlet with an outlet on either side are provided in a regular patternaround the final element. Arrows in liquid supply and liquid recoverydevices indicate the direction of liquid flow.

A further immersion lithography solution with a localized liquid supplysystem is shown in FIG. 4 . Liquid is supplied by two groove inlets oneither side of the projection system PS and is removed by a plurality ofdiscrete outlets arranged radially outwardly of the inlets. The inletsand outlets can be arranged in a plate with a hole in its center andthrough which the projection beam is projected. Liquid is supplied byone groove inlet on one side of the projection system PS and removed bya plurality of discrete outlets on the other side of the projectionsystem PS, causing a flow of a thin-film of liquid between theprojection system PS and the substrate W. The choice of whichcombination of inlet and outlets to use can depend on the direction ofmovement of the substrate W (the other combination of inlet and outletsbeing inactive). In the cross-sectional view of FIG. 4 , arrowsillustrate the direction of liquid flow in to inlets and out of outlets.

Another arrangement which has been proposed is to provide the liquidsupply system with a liquid confinement member which extends along atleast a part of a boundary of the space between the final element of theprojection system and the substrate table. Such an arrangement isillustrated in FIG. 5 . The liquid confinement member is substantiallystationary relative to the projection system in the XY plane, thoughthere may be some relative movement in the Z direction (in the directionof the optical axis). A seal is formed between the liquid confinementmember and the surface of the substrate. In an embodiment, a seal isformed between the liquid confinement member and the surface of thesubstrate and may be a contactless seal such as a gas seal. Such asystem is disclosed in United States patent application publication no.US 2004-0207824.

The fluid handling structure 12 includes a liquid confinement member andat least partly contains liquid in the space 11 between a final elementof the projection system PS and the substrate W. A contactless seal 16to the substrate W may be formed around the image field of theprojection system so that liquid is confined within the space betweenthe substrate W surface and the final element of the projection systemPS. The space is at least partly formed by the fluid handling structure12 positioned below and surrounding the final element of the projectionsystem PS. Liquid is brought into the space below the projection systemand within the fluid handling structure 12 by liquid inlet 13. Theliquid may be removed by liquid outlet 13. The fluid handling structure12 may extend a little above the final element of the projection system.The liquid level rises above the final element so that a buffer ofliquid is provided. In an embodiment, the fluid handling structure 12has an inner periphery that at the upper end closely conforms to theshape of the projection system or the final element thereof and may,e.g., be round. At the bottom, the inner periphery closely conforms tothe shape of the image field, e.g., rectangular, though this need not bethe case.

In an embodiment, the liquid is contained in the space 11 by a gas seal16 which, during use, is formed between the bottom of the fluid handlingstructure 12 and the surface of the substrate W. The gas seal is formedby gas, e.g. air, synthetic air, N₂ or another inert gas. The gas in thegas seal is provided under pressure via inlet 15 to the gap betweenfluid handling structure 12 and substrate W. The gas is extracted viaoutlet 14. The overpressure on the gas inlet 15, vacuum level on theoutlet 14 and geometry of the gap are arranged so that there is ahigh-velocity gas flow 16 inwardly that confines the liquid. The forceof the gas on the liquid between the fluid handling structure 12 and thesubstrate W contains the liquid in a space 11. The inlets/outlets may beannular grooves which surround the space 11. The annular grooves may becontinuous or discontinuous. The flow of gas 16 is effective to containthe liquid in the space 11. Such a system is disclosed in United Statespatent application publication no. US 2004-0207824.

The example of FIG. 5 is a localized area arrangement in which liquid isonly provided to a localized area of the top surface of the substrate Wat any one time. Other arrangements are possible, including fluidhandling systems which make use of a single phase extractor or a twophase extractor as disclosed, for example, in United States patentapplication publication no US 2006-0038968.

Another arrangement which is possible is one which works on a gas dragprinciple. The so-called gas drag principle has been described, forexample, in United States patent application publication nos. US2008-0212046, US 2009-0279060, and US 2009-0279062. In that system theextraction holes are arranged in a shape which desirably has a corner.The corner may be aligned with the stepping or scanning directions. Thisreduces the force on the meniscus between two openings in the surface ofthe fluid handing structure for a given speed in the step or scandirection compared to a fluid handling structure having two outletsaligned perpendicular to the direction of scan.

Also disclosed in US 2008-0212046 is a gas knife positioned radiallyoutside the main liquid retrieval feature. The gas knife traps anyliquid which gets past the main liquid retrieval feature. Such a gasknife may be present in a so called gas drag principle arrangement (asdisclosed in US 2008-0212046), in a single or two phase extractorarrangement (such as disclosed in United States patent applicationpublication no. US 2009-0262318) or any other arrangement.

Many other types of liquid supply system are possible. The presentinvention is neither limited to any particular type of liquid supplysystem, nor to immersion lithography. The invention may be appliedequally in any lithography. In an EUV lithography apparatus, the beampath is substantially evacuated and immersion arrangements describedabove are not used.

A control system 500 shown in FIG. 1 controls the overall operations ofthe lithographic apparatus and in particular performs an optimizationprocess described further below. Control system 500 can be embodied as asuitably-programmed general purpose computer comprising a centralprocessing unit and volatile and non-volatile storage. Optionally, thecontrol system may further comprise one or more input and output devicessuch as a keyboard and screen, one or more network connections and/orone or more interfaces to the various parts of the lithographicapparatus. It will be appreciated that a one-to-one relationship betweencontrolling computer and lithographic apparatus is not necessary. In anembodiment of the invention one computer can control multiplelithographic apparatuses. In an embodiment of the invention, multiplenetworked computers can be used to control one lithographic apparatus.The control system 500 may also be configured to control one or moreassociated process devices and substrate handling devices in a lithocellor cluster of which the lithographic apparatus forms a part. The controlsystem 500 can also be configured to be subordinate to a supervisorycontrol system of a lithocell or cluster and/or an overall controlsystem of a fab.

FIG. 6 schematically depicts an EUV lithographic apparatus 4100including a source collector apparatus SO. The apparatus comprises:

-   -   an illumination system (illuminator) EIL configured to condition        a radiation beam B (e.g. EUV radiation);    -   a support structure (e.g. a mask table) MT constructed to        support a patterning device (e.g. a mask or a reticle) MA and        connected to a first positioner PM configured to accurately        position the patterning device;    -   a substrate table (e.g. a wafer table) WT constructed to hold a        substrate (e.g. a resist-coated wafer) W and connected to a        second positioner PW configured to accurately position the        substrate; and    -   a projection system (e.g. a reflective projection system) PS        configured to project a pattern imparted to the radiation beam B        by patterning device MA onto a target portion C (e.g. comprising        one or more dies) of the substrate W.

These basic components of the EUV lithographic apparatus are similar infunction to the corresponding components of the lithographic apparatusof FIG. 1 . The description below mainly covers areas of difference andduplicative description of aspects of the components that are the sameis omitted.

In an EUV lithographic apparatus, it is desirable to use a vacuum or lowpressure environment since gases can absorb too much radiation. A vacuumenvironment can therefore be provided to the whole beam path with theaid of a vacuum wall and one or more vacuum pumps.

Referring to FIG. 6 , the EUV illuminator EIL receives an extreme ultraviolet radiation beam from the source collector apparatus SO. Methods toproduce EUV radiation include, but are not necessarily limited to,converting a material into a plasma state that has at least one element,e.g., xenon, lithium or tin, with one or more emission lines in the EUVrange. In one such method, often termed laser produced plasma (“LPP”)the plasma can be produced by irradiating a fuel, such as a droplet,stream or cluster of material having the desired line-emitting element,with a laser beam. The source collector apparatus SO may be part of anEUV radiation system including a laser, not shown in FIG. 6 , to providethe laser beam exciting the fuel. The resulting plasma emits outputradiation, e.g., EUV radiation, which is collected using a radiationcollector, disposed in the source collector apparatus. The laser and thesource collector apparatus may be separate entities, for example when aCO₂ laser is used to provide the laser beam for fuel excitation.

In such cases, the laser is not considered to form part of thelithographic apparatus and the radiation beam is passed from the laserto the source collector apparatus with the aid of a beam delivery systemcomprising, for example, suitable directing mirrors and/or a beamexpander. In other cases the source may be an integral part of thesource collector apparatus, for example when the source is adischarge-produced plasma EUV generator, often termed as a DPP source.

The EUV illuminator EIL may comprise an adjuster to adjust the angularintensity distribution of the radiation beam EB. Generally, at least theouter and/or inner radial extent (commonly referred to as σ-outer andσ-inner, respectively) of the intensity distribution in a pupil plane ofthe illuminator can be adjusted. In addition, the EUV illuminator EILmay comprise various other components, such as facetted field and pupilmirror devices. The EUV illuminator EIL may be used to condition theradiation beam EB, to have a desired uniformity and intensitydistribution in its cross section.

The radiation beam EB is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device. After being reflected from thepatterning device (e.g. mask) MA, the radiation beam EB passes throughthe projection system PS, which focuses the beam onto a target portion Cof the substrate W. With the aid of the second positioner PW andposition sensor PS2 (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theradiation beam EB. Similarly, the first positioner PM and anotherposition sensor PS1 can be used to accurately position the patterningdevice (e.g. mask) MA with respect to the path of the radiation beam EB.Patterning device (e.g. mask) MA and substrate W may be aligned usingmask alignment marks M1, M2 and substrate alignment marks P1, P2.

The depicted apparatus could be used the same modes as the apparatus ofFIG. 1 .

FIG. 7 shows the EUV apparatus 4100 in more detail, including the sourcecollector apparatus SO, the EUV illumination system EIL, and theprojection system PS. The source collector apparatus SO is constructedand arranged such that a vacuum environment can be maintained in anenclosing structure 4220 of the source collector apparatus SO. An EUVradiation emitting plasma 4210 may be formed by a discharge producedplasma source. EUV radiation may be produced by a gas or vapor, forexample Xe gas, Li vapor or Sn vapor in which the plasma 4210 is createdto emit radiation in the EUV range of the electromagnetic spectrum. Theplasma 4210 is created by, for example, an electrical discharge causingan at least partially ionized plasma. Partial pressures of, for example,10 Pa of Xe, Li, Sn vapor or any other suitable gas or vapor may berequired for efficient generation of the radiation. In an embodiment, aplasma of excited tin (Sn) is provided to produce EUV radiation.

The radiation emitted by the plasma 4210 is passed from a source chamber4211 into a collector chamber 4212 via an optional gas barrier and/orcontaminant trap 4230 (in some cases also referred to as contaminantbarrier or foil trap) which is positioned in or behind an opening insource chamber 4211. The contaminant trap 4230 may include a channelstructure. Contamination trap 4230 may also include a gas barrier or acombination of a gas barrier and a channel structure. The contaminanttrap or contaminant barrier 4230 further indicated herein at leastincludes a channel structure, as known in the art.

The collector chamber 4212 may include a radiation collector CO whichmay be a so-called grazing incidence collector. Radiation collector COhas an upstream radiation collector side 4251 and a downstream radiationcollector side 4252. Radiation that traverses collector CO can bereflected by a grating spectral filter 4240 to be focused in a virtualsource point IF. The virtual source point IF is commonly referred to asthe intermediate focus, and the source collector apparatus is arrangedsuch that the intermediate focus IF is located at or near an opening4221 in the enclosing structure 4220. The virtual source point IF is animage of the radiation emitting plasma 4210.

Subsequently the radiation traverses the illumination system IL, whichmay include a facetted field mirror device 422 and a facetted pupilmirror device 424 arranged to provide a desired angular distribution ofthe radiation beam 421, at the patterning device MA, as well as adesired uniformity of radiation intensity at the patterning device MA.Upon reflection of the beam of radiation 421 at the patterning deviceMA, held by the support structure MT, a patterned beam 426 is formed andthe patterned beam 426 is imaged by the projection system PS viareflective elements 428, 430 onto a substrate W held by the substratestage or substrate table WT.

More elements than shown may generally be present in illumination opticsunit IL and projection system PS. The grating spectral filter 4240 mayoptionally be present, depending upon the type of lithographicapparatus. There may be more mirrors present than those shown in theFigures, for example there may be from 1 to 6 additional reflectiveelements present in the projection system PS than shown in FIG. 7 .

Collector optic CO, as illustrated in FIG. 7 , is depicted as a nestedcollector with grazing incidence reflectors 4253, 4254 and 4255, just asan example of a collector (or collector mirror). The grazing incidencereflectors 4253, 4254 and 4255 are disposed axially symmetric around anoptical axis O and a collector optic CO of this type is preferably usedin combination with a discharge produced plasma source, often called aDPP source.

Alternatively, the source collector apparatus SO may be part of an LPPradiation system as shown in FIG. 8 . A laser LA is arranged to depositlaser energy into a fuel, such as xenon (Xe), tin (Sn) or lithium (Li),creating the highly ionized plasma 4210 with electron temperatures ofseveral 10's of eV. The energetic radiation generated duringde-excitation and recombination of these ions is emitted from theplasma, collected by a near normal incidence collector optic CO andfocused onto the opening 4221 in the enclosing structure 4220.

FIG. 9 depicts a substrate holder according to an embodiment of theinvention. It may be held within a recess in substrate table WT andsupports substrate W. The main body of the substrate holder 100 has theform of a flat plate, for example a disc substantially corresponding inshape and size to the substrate W. At least on a top side, in anembodiment on both sides, the substrate holder has projections 106,commonly referred to as burls. In an embodiment, the substrate holder isan integral part of the substrate table and does not have burs on thelower surface. The burs are not shown to scale in FIG. 9 .

In a practical embodiment, there can be many hundreds or thousands ofburls, e.g. more than 10,000 or more than 40,000 burls, distributedacross a substrate holder. e.g., of width (e.g., diameter) 200 mm, 300mm or 450 mm. The tips of the burls have a small area, e.g. less than 1mm². Thus the total area of all of the burs on one side of the substrateholder 100 is less than about 10%, e.g. 1-3% of the total area of thetotal surface area of the substrate holder. Because of the burlarrangement, there is a high probability that any particle that mightlie on the surface of the substrate, substrate holder or substrate tablewill fall between buds and will not therefore result in a deformation ofthe substrate or substrate holder.

The burl arrangement may form a pattern and/or may have a periodicarrangement. The burl arrangement can be regular or can vary as desiredto provide appropriate distribution of force on the substrate W andsubstrate table WT. The buds can have any shape in plan but are commonlycircular in plan. The burls can have the same shape and dimensionsthroughout their height but are commonly tapered. The distance that thebuds project from the rest of the surface of the main body 100 a of thesubstrate holder 100 is from about 1 μm to about 5 mm, desirably fromabout 5 μm to about 250 μm, from the rest of the surface of the mainbody 100 a of the substrate holder 100. The thickness of the main body100 a of the substrate holder 100 can be in the range of about 1 mm toabout 50 mm, desirably in the range of about 5 mm to 20 mm, typically 10mm.

In an embodiment of the invention, an upper surface of substrate holder100 is a smooth and flat initial surface for the formation of athin-film stack and a burl arrangement. In an embodiment, the uppersurface of substrate holder 100 is polished to form the smooth surface.In an embodiment, before applying a thin film layer as described herein,as described in U.S. patent application No. U.S. 61/576,627 filed on 16Dec. 2011, which is hereby incorporated by reference in its entirety,one or more techniques may be applied to smooth the surface of thesubstrate holder 100 to provide a surface on which a thin film layer maybe reliably be applied. See also U.S. patent application no. U.S. Ser.No. 13/323,520, filed 12 Dec. 2011, which is hereby incorporated byreference in its entirety, which refers to application of aplanarization layer over the surface. In an embodiment, planarization(e.g., having a planarization layer, polishing, etc.) is not necessarybefore burl formation as described herein. An embodiment of the presentinvention obviates planarization, for example where planarization mighthave been used to smooth a roughened surface which is roughened during amaterial removal process to form burls integral with the substratesupport. An embodiment of the invention may use an uncoated smoothplanar object on which the burs are directly deposited. The surface canbe smooth because it is planar and may, in an embodiment, be polishedbefore burl fabrication.

The substrate holder surface may, for example, be formed from SiC,SiSiC, Zerodur, Cordierite, or some other suitable ceramic orglass-ceramic material. An isolation layer is then deposited onto thesubstrate holder surface as a thin-film. The isolation layer may be anysuitable insulator. A conductive, e.g. metal, pattern is then depositedonto the isolation layer. The metal pattern may, for example, compriseone or more thin-film temperature sensors and/or heaters, and/or maycomprise a thin-film electrostatic clamp. The conductive pattern may beformed, for example, using lithography and etching, inkjet printing orany other suitable method. An isolation layer is then deposited onto theconductive pattern as a thin-film, thereby providing a smooth layer ofisolation material. Following this, material which is used to form budsis provided on the isolation layer. The burl material is patterned andetched (e.g. using a lithography and etching technique), thereby forminga set of buds in a desired arrangement or pattern. Further methods offorming the buds are described below. Various methods to form the burlscan be used. Generally the manner of formation of the buds can bedetermined by suitable inspection of the completed substrate holder.

The above method may be used to provide one or more thin-filmtemperature sensors and/or heaters and/or a film for an electrostaticclamp, and in addition provide burs, on a substrate holder in a unitarymanner as a multi-layer structure. The method may be beneficial for atleast one of the following reasons.

It avoids the need to remove material from a blank to form the burls andtherefore it may not be necessary to provide a planarization layer toform a flat surface for formation of the thin-film stack. The layers areapplied on a smooth initial surface of the substrate holder 100.

The thickness of the deposited layers is well controlled during thedeposition. Therefore, in an embodiment having one or more sensorsand/or heaters, the separation between a thin-film temperature sensorand/or heater and the substrate W is well controlled and consistent.This means that the temperature can be accurately measured by thethin-film temperature sensor.

The method allows thin-film temperature sensors to be provided acrossthe surface of the substrate holder/table. Therefore, the temperature ofthe substrate W can be measured at a plurality of locations across thesubstrate W. A similar advantage can exist for thin-film heaters, namelythat they can be used to provide heating at a plurality of locationsacross the substrate W. Therefore, they can provide more accurateheating than conventional heaters. The combination of thin-film sensorsand thin-film heaters allows real-time measurement and control of thesubstrate temperature to be achieved.

In an embodiment having an electrostatic clamp, the separation betweenthe thin-film electrostatic clamp and the substrate is well controlledand consistent so that the clamping force applied by the electrostaticclamp is more consistent (compared with the force that would be appliedif the separation between the electrostatic clamp and a substrate wasless well controlled). This is beneficial because non-uniformity in theclamping force applied to the substrate should be avoided, sincenon-uniformity of the clamping force could cause distortion of thesubstrate.

So-called pin-holes or cracks, such as breaks in the crystallinestructure of a thin-film known as dislocations, might arise in athin-film layer, e.g. an isolation layer of an electrostatic clamp. Suchfaults might give rise to reduced performance or failure of a componentin the thin-film stack, e.g. poor isolation. In an embodiment, this maybeneficially be avoided by providing the isolation layer as several thinlayers stacked together, such that pin-holes or cracks in a particularisolation layer are at least partially filled in when the next isolationlayer is deposited. The probability of a fault in one layer overlappinga fault in another layer is small.

Beneficially, the buds may be formed with very consistent dimensions, inparticular so that the variation between heights of different burs isvery small. Short burs can be formed (e.g. shorter than 20 μm, shorterthan 15 μm, shorter than 5 μm or shorter than 3 μm). Shorter burs arebeneficial because they increase the heat transfer between the substrateand the substrate holder. The gap between the top of the substrateholder away from the burls and the supported surface of a substrate onthe substrate holder is smaller than a support with a greater height.Such a small gap facilitates the transfer of heat from a temperatureconditioning element (e.g., heater) to the supported substrate. Theminimum burl height is determined by the variations in the total heightof the thin-film stack and the amount of unflatness of the substrate andsubstrate holder. In an embodiment the burl height is greater than orequal to 1 μm or 2 μm.

The burls can have a width (e.g., diameter) less than or equal to 0.5mm. In an embodiment the burs have a width (e.g., diameter) in the rangeof from about 250 μm to about 500 μm. The spacing between burls isbetween about 1.5 mm to about 3 mm.

Beneficially, an embodiment of the present invention enables that thearrangement of components in the thin-film stack is not constrained bythe position of the buds. Greater design freedom may be thereforeprovided than if the components must be placed around the burls, forexample if the buds are present on the substrate holder before athin-film layer of the electrical device is formed. If it is desired toground a burl, in an embodiment of the invention, a conductor, e.g. avia can be provided in the top isolation layer in the thin-film stack toconnect the burl to a grounding line. Additionally, or alternatively,one or more grounding lines can be provided on top of the thin-filmstack.

Further, an embodiment of the invention allows use of a wider range ofmaterials for the substrate holder. Materials that are not suitable forprevious methods of forming buds or substrate holders can be used in anembodiment of the invention. In an embodiment, it is possible to usematerial such as cordierite, a low CTE glass-ceramic, which cannoteasily be machined to form burls. Cordierite has good properties, suchas a high Young's modulus of about 125 Gpa and low thermal conductivityof about 3 W/mK, for use in a substrate holder.

A substrate holder manufactured according to an embodiment of theinvention can have a long usable life time due to robust manufacturingmethods. An embodiment of the invention can exhibit desirable wearproperties, for example good wear resistance and therefore lowgeneration of particular contaminants. Beneficially, an embodiment ofthe invention can avoid the need for coating the substrate holder.

A thin-film component may have a layer thickness in the range of fromabout 2 nm to about 100 μm. Such a thin film component may have one or aplurality of layers. Each layer may be formed by a process includingchemical vapor deposition, physical vapor deposition (e.g. sputtering),dip coating, spin coating and/or spray coating. In an embodiment, acomponent formed on the substrate holder comprises a thin-film stack,i.e. including a plurality of thin-film layers. Such components aredescribed further below. Although reference in this description is to athin film stack formed on the top surface of a substrate holder, thethin film stack may be formed on the undersurface of the substrateholder, or on a substrate table beneath a substrate holder, or on anyother surface of the substrate table or substrate holder, including asurface of an integral substrate holder and substrate table.

An electronic or electric component to be formed on the substrate tablecan include, for example, an electrode, a resistive heater and/or asensor, such as (in a non-limiting list) a strain sensor, a magneticsensor, a pressure sensor, a capacitive sensor or a temperature sensor.A heater and sensor can be used to locally control and/or monitor thetemperature of the substrate holder and/or substrate so as to reduceundesired or induced desired temperature variation and stress in thesubstrate holder or substrate. Desirably, the heater and sensor areformed on, around and/over the same region as each other. It isdesirable to control temperature and/or stress of the substrate in orderto reduce or eliminate imaging errors such as overlay errors due tolocal expansion or contraction of the substrate. For example, in animmersion lithography apparatus, evaporation of residual immersionliquid (e.g., water) on the substrate can cause localized cooling, mayapply a heat load to the surface on which the liquid is located, andhence shrinkage of the substrate. Conversely, the energy delivered tothe substrate by the projection beam during exposure can causesignificant heating and therefore expansion of the substrate.

In an embodiment, the component to be formed is an electrode for anelectrostatic clamp. In electrostatic clamping, an electrode provided onthe substrate table and/or substrate holder is raised to a highpotential, e.g. from 10 to 5,000 V. The substrate can be grounded orfloating. Electrostatic forces in the electric field generated by theelectrode attract the substrate to the substrate table and/or holder toprovide a clamping force. This is described further below.

One or more electrical connections can be provided to connect theelectric or electronic component on the substrate holder to a voltagesource (not shown for convenience). If the component is an electrostaticclamp, the electrode on the substrate has an electrical connection tothe voltage source. The component may be on a top surface of thesubstrate support. At least part of the electrical connection may passthrough the body of the substrate support as described in U.S. patentapplication No. U.S. 61/555,359, filed on 3 Nov. 2011, which is herebyincorporated by reference in its entirety.

In an embodiment, one or more localized heaters 101 are controlled bycontroller 103 to provide a desired amount of heat to the substrateholder 100 and substrate W to control the temperature of the substrateW. One or more temperature sensors 102 are connected to controller 104which monitors the temperature of the substrate holder 100 and/orsubstrate W. Arrangements using one or more heaters and temperaturesensors to locally control the temperature of a substrate are describedin copending U.S. patent application publication no. US 2012-0013865,which document is incorporated herein by reference in its entirety. Thearrangements described therein can be modified to make use of aresistive heater and temperature sensor as described herein.

FIG. 10 shows steps A to F of a method to form a substrate holderaccording to an embodiment of the invention. Starting with a flat blankof suitable shape and thickness to form the substrate holder 100, shownin A, a thin-film stack 110 is formed, as shown in B (see also FIG. 9 ).The thin-film stack can be formed in several sub-steps. The firstsub-step is to form a bottom isolation layer on the surface of thesubstrate holder 100. As mentioned above, this may include providingseveral thin-film layers of isolation material (e.g. to reduce oreliminate pinholes and cracks). Such a method can maintain and ensurethe smoothness of the surface on which one or more further layers may beformed.

The second sub-step is to form one or more various different componentsas described below. The formed layer may be a patterned layer of, forexample, conductive material. The conductive material desirably includesa metal. This second sub-step may itself comprise a series of sub-steps,for example lithographic patterning and etching. The patterning andetching may pattern the layer to form the one or more components in thelayer.

The third sub-step is to form the top isolation layer on top of themetal pattern. The top isolation layer electrically isolates thepatterned conductive layer from electrical conduction to an objectapplied from above or a short circuit to another part of the patternedlayer. Again, this may include providing several thin-film layers ofisolation material. Depending on the complexity of the component, one ormore further conductive and isolating layers may be applied.

Next, as shown at C, a layer of burl-forming material 111 is provided onthe thin-film stack 110. The layer of burl-forming material is to bepatterned to form the burs in one or more subsequent steps of themethod. The burl-forming material can be selected from the groupcomprising diamond such as diamond-like carbon (DLC), SiC, SiO₂, TiN andCrN. To form the burls from layer 111, a patterned metal mask 112 isformed on the top isolation layer as shown at D. This may be achievedvia a combination of metal layer and photo-resist deposition andlift-off via lithography and selective etching. Then, layer 111 is dryetched, for example by directing a plasma (e.g. oxygen and/or fluorine)through the metal mask 112 to arrive at the state shown at E. In thestate shown in E, the parts of the layer of burl forming material 111which are not covered by the patterned metal mask are removed, e.g.etched, away. The top of the thin-film stack 110, i.e. a top surface ofan isolation layer, is thus revealed from under the layer of burlforming material. Removal of the metal mask by a conventional methodleaves the finished substrate holder as shown in F. If desired, acoating can be provided on top of the buds 106. It is possible to adjustor correct the shape and/or profile of the burls using, for example, ionbeam figuring.

A further method to form a substrate holder is a sputtering method shownin FIG. 11 . The second method is similar to that of FIG. 10 and has thesame steps A and B. At step C, a negative tone photo-resist 120 isprovided. Then the negative tone photo-resist is patterned at D to formopenings in the resist layer. The openings are at locations at whichburls are to be formed (i.e. the patterned resist 120′ forms a mask).The openings in the negative tone photo-resist 120 reveal the surface ofthe thin-film stack, e.g. the outermost isolation layer 110. Burlmaterial 121 is then provided, e.g. by sputter deposition, at step E,such that it fills the openings in the resist layer. The bud materialforms a layer over the resist layer 120. The excess burl material isremoved by, e.g., polishing, to expose the resist layer 120′. Then theremaining resist 120′ is removed. The bud material is left behindforming an arrangement of buds 106, as shown at F. In this method, thesame materials can be used to form the burls as in the above describedmethod.

A further method of forming a substrate holder uses direct deposition,as shown in FIG. 12 . In this method, steps A and B are the same as forthe methods of FIG. 10 and/or FIG. 11 . In step C, a hard-mask 130 isprovided over the substrate holder/table surface. The mask is patternedwith openings in negative to the desired pattern of buds to be formed onthe thin-film stack 110. The burl material is then supplied through thehard mask 130. The burl material deposits on the surface of thethin-film stack, e.g. the outermost isolation layer, to form a deposithaving the desired bud pattern, for example an array of burls 106. Inthis method, the same materials can be used to form the burls as in theabove described methods.

In a further method, the burls 106 are deposited directly onto theinitial surface of the substrate holder. This is depicted in FIG. 18 .The layers of the thin-film stack 110 are formed on the initial surfaceof the substrate holder 100 before the buds are deposited. Steps A and Bare the same as for the methods described with respect to FIGS. 10, 11and/or 12 . The thin-film stack is selectively etched according to apattern to reveal parts of the initial surface. Selectively etching thethin-film stack can be performed by depositing a photo-resist layer 140in step C, then selectively exposing the photo-resist and developing it.This forms a patterned resist layer 140′ having openings at locationscorresponding to the positions at which buds are to be formed as shownin step D. The next step, step E, is to etch the thin-film stack throughthe openings in the patterned resist layer 140′. Buds 106 are thenformed at step F in the openings in the thin-film stack 110 (before orafter removal of resist layer 140′).

Various processes can be used to form the burls 106 in this method. Forexample, it is possible to use steps D to F of the method of FIG. 11 orstep C of the method of FIG. 10 or step C of the method of FIG. 12 . Inanother process, material for forming the buds is deposited in a layer,covering the thin-film stack and filling the openings in the thin-filmstack. The burl material covering the thin-film stack is removed forexample by etching through a mask. The buds can then be shaped. Thismethod can be desirable, although it might have more steps than othermethods, because the burl material can be of similar material (i.e.ceramic) or even the same material as the substrate holder. Similarmaterials are more likely to form a more secure bond than dissimilarmaterials.

In a further method, explained below with reference to FIGS. 19A to 19E,laser sintering is used to form the burls. This method starts with aflat plate of the desired shape which forms the main body 400 of thesubstrate holder. In an embodiment the plate is formed of SiSiC butanother material such as Invar™, Zerodur™, ULET™, fused silica,cordierite, boron nitride, silicon nitride, aluminum nitride (AlN)and/or SiC can also be used. Desirably, an initial surface 400 a of theplate is ground and/or polished to a desired degree of flatness. In anembodiment, the initial surface is cleaned, e.g. with ozone, but thisstep may be omitted in many cases. In an embodiment, the initial surfaceis treated to promote adherence of one or more subsequent layers, e.g.by application of a primer layer, but again this step may be omitted inmany cases. On the plate, an isolation layer 410 is applied to isolateone or more metal layers to be formed above it from the main body of thesubstrate holder and to further improve flatness (if desired). Theisolation layer 410 may be made of BCB applied by spin or spray coatingas described above or of SiO₂ applied by a PECVD process, or othersuitable material, e.g. as described above. On top of the isolationlayer, a metal layer 440 is applied, e.g. by PVD, to arrive at thesituation shown in FIG. 19A.

The metal layer is then patterned. e.g. by lithography and selectiveetching, e.g. a wet etch, to define the desired pattern to form adesired component, e.g. one or more electrodes, sensors and/or heaters.This step also removes the metal layer in an area where buds are to beformed in a subsequent step. At this stage, the substrate holder is asillustrated in FIG. 19B.

Over the patterned metal layer, a second isolation or dielectric layer450 is applied and one or more openings through to the base layer, i.e.through both isolation layers, are formed in the locations where burlsare desired. The substrate holder is now as illustrated in FIG. 19C.Optionally, the exposed area 400 b of the initial surface of the mainbody 400 is cleaned, e.g. with ozone, and/or treated, e.g. byapplication of a primer layer to promote adhesion of the buds which areto be formed subsequently. Burls 406 are now formed in the openingthrough the thin film stack by a laser sintering process. There are twotypes of laser sintering methods, both are usable in the embodimentdescribed herein.

In the first method, a thin layer of powder is applied to the area whereburls are to be formed then one or more laser beams are used toselectively sinter the powder in the area where the burls are to beformed. When that is complete, another thin layer of powder is appliedand selectively heated and sintered. This is repeated so that the bud isbuilt up layer by layer. Since the sintering pattern can be varied ateach layer, the burl can be built up with any desired shape and profile.In this method, the powder may be applied over a large area and multipleburls formed simultaneously or concurrently. Alternatively, powder maybe applied to a small area and each bud formed independently. Furtherdetails of this process can be found in “Laser micro sintering—a qualityleap through improvement of powder packing” by A Streek et al publishedathttp://laz.htwm.de/43_rapidmicro/55_Ver%C3%B6ffentlichungen/Laser%20micro%20sintering/a20-%20a%20quality%20leap%20through%20improvement%20of%20powder%20packing.pdf.

In the second method, powder is jetted in an inert gas over the areawhere a burl is to be formed while one or more laser beams irradiate theprecise locations where burs are to be formed. Powder selectivelyadheres to the positions irradiated by the laser beam and by suitablyshifting the point of radiation, a burl of desired profile can be builtup. Further details of this process can be found in “MICRO-CLADDINGUSING A PULSED FIBRE LASER AND SCANNER” by S. Kloetar et al published athttp://laz.htwm.de/43_rapidmicro/55_Ver%C3%B6ffentlichungen/Microcadding_LPM2010.pdf.

As with other sintering techniques, laser sintering works by partiallymelting particles of the powder so that they adhere together when theycool. Laser sintering has an advantage that the controlled applicationof the laser beam allows for spatial control of where sintering takesplace. In both methods described above, the powder can be pre-heated toa temperature close to the relevant melting point so that less energyneed be applied by the laser to complete the sintering. A wide varietyof materials can be used in sintering techniques. The powder can beformed of a single material, e.g. a metal such as titanium, asemiconductor such as silicon or a ceramic such as fused silica,cordierite and/or aluminum nitride. In a further embodiment, the powderis made of two or more components. One component has a relatively lowmelting point which melts to form a matrix in which the otherparticulate component(s) is(are) embedded. The matrix-forming componentof the powder can be provided as separate particles or as a coating onparticles of other materials. The matrix forming compound can be any ofthe single materials mentioned above. The particulate component can beone or more components selected from the group comprising cubic boronnitride, silicon nitride, silicon carbide, titanium nitride, titaniumcarbide and/or diamond, e.g. DLC. The sintering process can be carriedout in an inert atmosphere or a vacuum to help prevent chemical changeto the material being sintered or in a controlled atmosphere to promotea chemical change.

Thus, the material from which the burl is to be formed can be selectedfrom a wide range of materials to provide one or more desired propertiessuch as strength of adherence to the material of the base body of thesubstrate holder. Desirably, the burl is made of the same material as,or a material compatible with, the material of the main body of thesubstrate holder. For example, it is generally desirable that the burlbond well to the base material of the main body of the substrate so asto provide longevity and robustness in use. In some applications, it isdesirable that the buds have high thermal conductivity to assist intemperature conditioning of the substrate. In other applications, a lowthermal conductivity can be desirable in order to isolate the substrate.Other relevant properties of the burls that can be affected throughchoice of material include electrical conductivity, dielectric strengthand wear resistance.

The laser sintering technique for forming the buds generally results ina rough upper surface to the buds as depicted in FIG. 19D. If so, it isdesirable to perform a final polishing step so as to provide a smoothupper surface to the burls as illustrated FIG. 19E. In some cases, e.g.if the final polishing is performed with a coarse-grained slurry, itmight be desirable to first protect the thin film stacks with anadditional coating. However this is often not necessary, for examplewhere the thin film stack contains only electrodes for clampingpurposes.

A further advantage of the laser sintering process is that it allows thecomposition of a burl to be varied through its height. It is thereforepossible to manufacture burls having sections or layers of a differentcomposition and/or property as illustrated in FIG. 20 . For example, alower part 406 a of the burl can be formed of material that bonds wellto the material of the base body of the substrate holder, while theupper part 406 b of the burl is formed of a material having an improvedwear property. For example, particles of diamond e;g. DLC can beincluded in the upper part 406 b of the burl to improve wear resistance.In an embodiment a burl is formed with more than two distinct layers. Inan embodiment a burl is formed with a gradual change in composition,content or material property through at least a part of its height.

It is also possible to vary the composition of the powder to be sinteredin a direction substantially parallel to the surface on which the budsis being formed. In the powder layer method of sintering, this may beachieved through variation of the composition of the powder within eachlayer of powder as it is applied. In the powder jetting method this maybe achieved through variation of the composition of the jetted powderwith time in synchronization with movement of the point of laserirradiation. Varying the material composition of the bud in a directionsubstantially parallel to the surface on which it is formed, optionallyin addition to variation in the height direction, can allow fine controlover one or more mechanical and/or other properties of the burl, e.g.stiffness.

An advantage of this laser sintering embodiment is that burs can beformed with almost any shape in three dimensions. In an embodiment, aburl has a constant cross-section throughout its height. In anembodiment, a burl tapers away from the main body of the substrateholder. In an embodiment, the cross-section of a burl varies withheight. In an embodiment, a burl has a cross-section substantiallyparallel to the surface of the main body of the substrate holder that isselected from the group consisting of circle, square, rectangle, oval,rhombus and/or “racetrack” or “stadium” shape. A “racetrack” or“stadium” shape has two straight parallel sides joined by curves, e.g.semicircles.

Although specific methods have been described above which may be used toform burls, sensors, heaters and an electrostatic clamp, in a unitarymanner as a multi-layer structure, any other suitable method may beused. In an embodiment of the invention, a thin-film stack is providedon only one side of the substrate holder. In an embodiment, thin-filmstacks are provided on both sides of the substrate holder. In anembodiment, buds are provided on both sides of the substrate holder. Ifbuds are provided on a side of the substrate holder that does not have athin-film stack thereon, any convenient method for forming the buds onthat side can be used. Such methods include those described above aswell as other methods, such as machining that involve removal ofmaterial from the main body. Deposition of the layers can be achieved byPlasma Enhanced Chemical Vapor disposition (PE CVD), Chemical VaporDeposition (CVD), Physical Vapor Deposition (PVD) and/or sputtering. Themethod used for the deposition depends upon the material(s) beingdeposited. The thickness variation obtained by the deposition can besmaller than 5 percent.

A substrate holder for use in a conventional (DUV) lithographicapparatus (e.g. an immersion lithographic apparatus) is desirablyprovided with one or more thin-film temperature sensors and/or thin-filmheaters.

A substrate holder for use in an EUV lithographic apparatus is desirablyprovided with a thin-film electrostatic clamp and optionally one or morethin-film temperature sensors and/or thin-film heaters.

Examples of thin-film stacks, incorporating electric or electroniccomponents, that are usable in embodiments of the invention are shown inFIGS. 13 to 15 and described below.

FIG. 13 shows a thin-film stack comprising an isolation layer 201, oneor more metal lines 202 and isolation layer 203. Isolation layer can beformed of PE CVD (Plasma Enhanced Chemical Vapor Deposition) SiO_(x).The isolation layer 201 desirably has a thickness greater than 0.1 μm.Desirably it has a thickness less than 10 μm. In an embodiment theisolation layer has a thickness of 5 μm.

On top of the isolation layer, one or more metal lines 202 are depositedby photolithography or metal deposition and etching through a hard mask.Metal line 202 desirably has a width greater than 20 μm. The maximumwidth of the metal line is determined by its function and availablespace. Other methods of forming the metal line are usable. In the caseof a heater and/or sensor, one or more wide metal lines (e.g. about 1500μm) can be used as a heating element and a narrow metal line (e.g. about100 μm) can be used as a sensor element. For an electrostatic clamp, twohalves of continuous metal film (but isolated from the burl tops)separated by approximately 500 μm from each other can be deposited toform positive and negative elements of the electrostatic clamp. Metalline 202 desirably has a layer thickness greater than about 20 nm,desirably greater than about 40 nm. Metal line 202 desirably has a layerthickness less than or equal to about 1 μm, desirably less than about500 nm, desirably less than about 200 nm.

For a heater and/or sensor, a patterned metal line 202 can have multiplemetal layers, for example titanium (Ti) and platinum (Pt). In anembodiment a layer of 10 nm thick titanium provides improved adhesionfor a platinum line of approximately 250 thickness. Patterning ofmultiple layers can be achieved using a combination of photo-resistdeposition, PVD for metal film deposition and a lift-off process. For aheater, a wide chromium line (˜1500 μm) can be deposited by Cr filmdeposition (PVD) and selective Cr etching using a mask. For anelectrostatic clamp, an electrode can consist of aluminum, chromium orany other conductive material. An electrode can be formed by PVD orsputtering. An alloy of these metals in any suitable combination canalso be used.

It is desirable to electrically isolate a deposited metal line fromabove and protect it from particle depositions, scratches and oxidation.Hence a top or outermost isolation layer is deposited on the metal line202. For a heater or a sensor, the isolation layer can be deposited byspray coating of BCB (40% bis-benzocyclobutene dissolved in1,3,5-trimethyl benzene) or NN 120 (20% perhydropolysilazane in di-butylether); SiO_(x) as described previously; or a combination of sprayedlayers and SiO_(x). In the case of an electrostatic clamp, a topisolation layer also provides dielectric strength so that the clampingpressure and gap between the layer stack and substrate can be tuned todesired values. In an embodiment, the top isolation layer for anelectrostatic clamp has, or consists of, spray coated polymer layers ofBCB, NN 120 (or combination of these two sprayed materials), SiO_(x)alone, a combination of spray coated polymer layers and SiO_(x), orparylene (CVD) alone. The top isolation layer 203 desirably has a layerthickness greater than about 0.1 μm, desirably greater than about 1 μm.The top isolation layer 203 desirably has a layer thickness less thanabout 10 μm, desirably less than about 3 μm, for a heater or a sensor.For an electrostatic clamp, the top isolation layer desirably has alayer thickness less than about 100 μm, desirably less than about 20 μm.In an embodiment the thickness is in a range from about 10 to about 60μm.

Table 1 shows an examples of suitable materials per layer in order tobuild a thin-film stack. Each layer may be formed of one of the listedmaterials or a combination of two or more materials. Methods ofapplication are indicated in parenthesis.

TABLE 1 Appl. Layer 1. Heater only 2. Sensor & Heater 3. Clamp BottomBCB (spray) BCB (spray) BCB (spray) isolation CAG 37 (spray) CAG 37(spray) CAG 37 (spray) NN 120 (spray) NN 120 (spray) NN 120 (spray)SiOx, SiOx, SiOx (PVD/CVD/PECVD/ (PVD/CVD/PECVD/ (PVD/CVD/PECVD/Sputtering) Sputtering) Sputtering) Polyimide (spray) Polyimide (spray)Parylene (CVD) Polyimide (Spray) Metal layer Chrome Platinum Chrome,(PVD/CVD/Sputtering) (PVD/CVD/Sputtering Aluminum lift-off)(PVD/CVD/Sputtering) Top BCB (spray) BCB (spray) BCB (spray) IsolationCAG 37 (spray) CAG 37 (spray) CAG 37 (spray) NN 120 (spray) NN 120(spray) NN 120 (spray) SiOx SiOx SiOx (PVD/CVD/PECVD/ (PVD/CVD/PECVD/(PVD/CVD/PECVD/ Sputtering) Sputtering) Sputtering) Polyimide (spray)Polyimide (spray) Parylene (CVD) Polyimide (spray)

Table 2 shows examples of specific function and requirements per layerfor the applications:

TABLE 2 Appl. Layer 1. Heater only 2. Sensor & Heater 3. Clamp Bottommoderate high electrical high dielectric isolation electrical isolation(for sensor strength isolation resolution) high volume low temperaturelow temperature resistivity difference difference low temperature acrossthe layer across the layer difference short response short responseacross the layer time time Metal layer heater power sensor sensitivityhigh voltage sensor stability requirements heater power (electrodelayout) Top encapsulation encapsulation high dielectric isolationstrength high volume resistivity low temperature difference across thelayer

Thin-film technology offers an overlay improvement and a cost effectivesolution for heater and/or sensor development. Metal pattern designs canbe modified easily (by modifying mask designs). If a platinum (Pt) metallayer is used, a titanium adherence layer can first be applied toimprove adhesion of the Pt layer. For electrostatic clamps, any suitablemetal having a low resistance can be used.

Dielectric layers can be deposited by spray coating, spin coating and PECVD techniques. Spray coating is particularly suitable for depositing apolymer based layer (dissolved in organic solvent) such as a BCB and/orNN 120 layer. But a first sprayed layer may suffer from surface defectssuch as pin-holes (because of local impurities) and cracks (most likelybecause of stresses induced in the layers) if too thick a layer isdeposited. It is possible to reduce the effect of these surfaceimperfections by combining different deposition processes. In anembodiment of the invention, layers can be applied using an inkjet orbubblejet printing technique. This allows for local control of the layerthickness, which can be useful to correct for local variation in thesurface contour or the surface roughness of the substrate holder. Thesetechniques also enable patterning of a conductive layer using aconductive ink. A combination of different materials and/or layerformation techniques can be desirable as a defect in one layer can becured by another layer.

A thin-film stack 110 b shown in FIG. 14 by way of example comprises, inorder above the base layer 100, first isolation layer 201, a first metallayer (e.g., metal lines) 202, second isolation layer 203, second metallayer (e.g., metal lines) 204 and third isolation layer 205. Each ofthese layers can be formed by a suitable method as described herein. Oneor more further metal layers and one or more further isolation layerscan also be provided. In this embodiment, the use of two or more stackedmetal layers allows the formation of two or more stacked components,e.g. sensors. Stacked sensors can provide increased isolation fromnoise. In an embodiment, one or more metal layers can act as shieldingfor one or more signal lines in another layer.

A thin-film stack 110 c shown in FIG. 15 comprises first isolation layer201 and second isolation layer 203 either side of the electronic orelectric components 206, 207. That is the components are sandwichedbetween the first and second isolation layers. Multiple components maybe formed in a single layer on the substrate. In an embodiment, each ofthe components 206, 207 is formed by a plurality of layers. For examplesuccessive layers of the component may consist of metal-amorphoussilicon-metal. In such an embodiment, one or more of the components 206,207 forms a transistor or other logic device. Such logic devices can beused to control an array of heaters disposed across the surface of thesubstrate holder without requiring individual connections to eachheater. The transistors can be arranged at the intersection of word andbit lines and each connected to an associated heater to form an activematrix.

FIGS. 16 and 17 depict, in cross-section, electrostatic clampingarrangements of substrate holders according to embodiments of theinvention.

In the substrate holder of FIG. 16 , a thin-film stack—comprising firstisolation layer 201, electrode layer 301 and second isolation layer203—is formed on the main body 100 of the substrate holder. Electrodelayer 301 is shown in this view as three separate parts but these areelectrically continuous. Optional vias 302 (i.e. electrical pathways)pass through the thin-film stack to electrically connect the main body100 to burs 106 formed on the thin-film stack as described above. Avoltage source 300 applies a potential, e.g. in the range of 10 to 5,000V to the electrode layer 301. The main body 100 is grounded, as are theburls 106 and substrate if the vias 302 are provided. The electric fieldgenerated by the potential applied to the electrode layer 301 causes anelectrostatic force to clamp the substrate W to the substrate holder.

The substrate holder of FIG. 17 is similar except that the vias 302 areomitted and electrode layer 301 is divided into two (or more)electrically separate parts. The voltage source applies a potentialdifference, e.g. in the range of 10 to 5,000 V, between two parts of theelectrode layer 301. One of the parts of the electrode layer 301 isgrounded. The resulting field generates an electrostatic clamping forcein a similar manner.

One or more sensors and any associated burls are desirably arranged toas to minimize pickup of electromagnetic interference, as described incorresponding U.S. patent application No. U.S. 61/576,627, filed on 16Dec. 2011, which document is incorporated by reference in its entirety.

While discussion herein has focused on heaters, an embodiment of theinvention applies to an electric or electronic component that generallyprovides heat transfer function. Accordingly, the electric or electroniccomponent may be, for example, a cooler or a combination ofheater/cooler.

As will be appreciated, any of the above described features can be usedwith any other feature and it is not only those combinations explicitlydescribed which are covered in this application.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of ICs, it should beunderstood that the lithographic apparatus described herein may haveother applications in manufacturing components with microscale, or evennanoscale features, such as the manufacture of integrated opticalsystems, guidance and detection patterns for magnetic domain memories,flat-panel displays, liquid-crystal displays (LCDs), thin-film magneticheads, etc. The skilled artisan will appreciate that, in the context ofsuch alternative applications, any use of the terms “wafer” or “die”herein may be considered as synonymous with the more general terms“substrate” or “target portion”, respectively. The substrate referred toherein may be processed, before or after exposure, in for example atrack (a tool that typically applies a layer of resist to a substrateand develops the exposed resist), a metrology tool and/or an inspectiontool. Where applicable, the disclosure herein may be applied to such andother substrate processing tools. Further, the substrate may beprocessed more than once, for example in order to create a multi-layerIC, so that the term substrate used herein may also refer to a substratethat already contains multiple processed layers.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm).

The term “lens”, where the context allows, may refer to any one orcombination of various types of optical components, including refractiveand reflective optical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention, at least in the form of amethod of operation of an apparatus as herein described, may bepracticed otherwise than as described. For example, the embodiments ofthe invention, at least in the form of a method of operation of anapparatus, may take the form of one or more computer programs containingone or more sequences of machine-readable instructions describing amethod of operating an apparatus as discussed above, or a data storagemedium (e.g. semiconductor memory, magnetic or optical disk) having sucha computer program stored therein. Further, the machine readableinstruction may be embodied in two or more computer programs. The two ormore computer programs may be stored on one or more different memoriesand/or data storage media.

Any controllers described herein may each or in combination be operablewhen the one or more computer programs are read by one or more computerprocessors located within at least one component of the lithographicapparatus. The controllers may each or in combination have any suitableconfiguration for receiving, processing and sending signals. One or moremultiple processors are configured to communicate with at least one ofthe controllers. For example, each controller may include one or moreprocessors for executing the computer programs that includemachine-readable instructions for the methods of operating an apparatusas described above. The controllers may include data storage media forstoring such computer programs, and/or hardware to receive such media.So the controller(s) may operate according to the machine readableinstructions of one or more computer programs.

An embodiment of the invention may be applied to substrates with a width(e.g., diameter) of 300 mm or 450 mm or any other size.

One or more embodiments of the invention may be applied to any immersionlithography apparatus, in particular, but not exclusively, those typesmentioned above, whether the immersion liquid is provided in the form ofa bath, only on a localized surface area of the substrate, or isunconfined on the substrate and/or substrate table. In an unconfinedarrangement, the immersion liquid may flow over the surface of thesubstrate and/or substrate table so that substantially the entireuncovered surface of the substrate table and/or substrate is wetted. Insuch an unconfined immersion system, the liquid supply system may notconfine the immersion liquid or it may provide a proportion of immersionliquid confinement, but not substantially complete confinement of theimmersion liquid.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more liquid inlets, one ormore gas inlets, one or more gas outlets, and/or one or more liquidoutlets that provide liquid to the space. In an embodiment, a surface ofthe space may be a portion of the substrate and/or substrate table, or asurface of the space may completely cover a surface of the substrateand/or substrate table, or the space may envelop the substrate and/orsubstrate table. The liquid supply system may optionally further includeone or more elements to control the position, quantity, quality, shape,flow rate or any other features of the liquid.

In a first aspect of the invention there is provided a substrate holderfor use in a lithographic apparatus, the substrate holder comprising: amain body having a surface; a thin-film stack provided on the surfaceand forming an electric component; and a plurality of burls provided onthe thin-film stack and having end surfaces to support a substrate.

The main body may be formed of a different material than the buds. Theor a component in the thin-film stack may be located at least partlybetween a burl and the main body. Buds may project from the thin-filmstack by a distance selected from the range of from 1 to 20 μm,desirably from the range of from 5 to 15 μm. The distance may be lessthan 5 μm, desirably less than 3 μm.

The burls may have been formed by a process selected from the groupconsisting of: deposition and selective etching; sputtering through apatterned resist layer; deposition through a hardmask; andlaser-sintering. The burls may be formed from a material selected fromthe group consisting of: diamond-like carbon, SiC, SiO₂, TiN and CrN. Atleast one burl may comprise a first layer of a first material and asecond layer of a second material that is different from the firstmaterial. The burls may be cylindrical. The burs may taper away from thethin-film stack. The main body may be formed from a material selectedfrom the group consisting of: Zerodur, Cordierite, SiC, AlN, SiSiC,ceramic and glass-ceramic.

The thin-film stack may include at least one via in electrical contactwith a burl. The thin-film stack may form a plurality of electriccomponents. A first electric component and a second electric componentof the plurality of electric components may be arranged in a singlelayer of the thin-film stack. A first electric component and a secondelectric component of the plurality of electric components may bearranged in two separate layers of the thin-film stack. The componentmay be a component selected from the group consisting of: an electrode,a heater, a sensor, a transistor and a logic device. The electrode maybe, in use, an electrode of an electrostatic clamp.

In a second aspect of the invention there is provided a substrate holderfor use in a lithographic apparatus, the substrate holder comprising: amain body having surface; a thin-film stack provided on the surface andforming an electronic or electric component, the thin-film stack havinga plurality of apertures formed therein; and a plurality of projections,each projection provided in an aperture of the thin-film stack, theplurality of projections being configured to support a substrate.

The surface of the main body may be the surface of a planarization layerof the main body.

In a third aspect of the invention there is provided a lithographicapparatus, comprising: a support structure configured to support apatterning device; a projection system arranged to project a beampatterned by the patterning device onto a substrate; and a substrateholder arranged to hold the substrate, the substrate holder beingaccording to the first or second aspect of the invention.

The lithographic apparatus may comprise a substrate table and whereinthe substrate holder is integrated into the substrate table.

In a fourth aspect of the invention there is provided a table for use ina lithographic apparatus, the table comprising: a main body having asurface; a thin-film stack provided on the surface and forming anelectronic or electric component; and a plurality of buds provided onthe thin-film stack and having end surfaces to support an object, forexample a substrate.

In a fifth aspect of the invention there is provided a table for use ina lithographic apparatus, the table comprising: a recess to receive asubstrate holder of the first or second aspect of the invention; and thesubstrate support.

In a sixth aspect of the invention there is provided a lithographicapparatus, comprising: a support structure configured to support apatterning device; a projection system arranged to project a beampatterned by the patterning device onto a substrate; and a tableaccording to the fourth or fifth aspects of the invention.

In a seventh aspect of the invention there is provided a devicemanufacturing method using a lithographic apparatus, the methodcomprising: projecting a beam patterned by a patterning device onto asubstrate while holding the substrate in a substrate holder, wherein thesubstrate holder comprises: a main body having a surface; a thin-filmstack provided on the surface and forming an electronic or electriccomponent; and a plurality of burls provided on the thin-film stack andhaving end surfaces to support the substrate.

In an eighth aspect of the invention there is provided a method ofmanufacturing a substrate holder for use in a lithographic apparatus,the method comprising: providing a main body having a surface; forming athin-film stack on the surface of the main body; and forming a pluralityof buds on the thin-film stack, the buds projecting from the stack andhaving end surfaces to support a substrate.

Forming the plurality of burls may comprise: forming a layer ofbud-forming material on the thin-film stack; forming a mask on the layerof burl-forming material; etching the burl-forming material through themask; and removing the mask.

Forming the plurality of burls may comprise: forming a mask having aplurality of apertures; providing a layer of burl-forming material toadhere to the thin-film stack through the apertures; and removing themask and any bud-forming material overlaying the mask. Providing thelayer of bud-forming material may comprise sputtering or vapordeposition. Forming the mask comprises: providing a layer ofradiation-sensitive resist; exposing the resist; and developing theresist. The burls may be formed from a material selected from the groupconsisting of: diamond-like carbon, SiC, SiO₂, TiN and CrN.

In a ninth aspect of the invention there is a method of manufacturing asubstrate holder for use in a lithographic apparatus, the methodcomprising: providing a main body having a surface; forming a thin-filmstack on the surface of the main body; forming a plurality of aperturesin the thin-film stack; and forming a plurality of burls in theapertures of the thin-film stack, the burs projecting from the stack andhaving end surfaces to support a substrate. Forming the plurality ofburls may comprise forming the burs by laser sintering.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1.-15. (canceled)
 16. A substrate holder for use in a lithographicapparatus, the substrate holder comprising: a main body having a firstside of the main body and a second side of the main body opposite to thefirst side; a plurality of first burs at the first side of the main bodyand having end surfaces to support a substrate in the lithographicapparatus, wherein each of the first burls comprise a lower body portionprotruding from the main body and an upper body portion above the lowerbody portion, wherein the lower body portions are a different materialthan the upper body portions, the upper body portions comprise amaterial selected from: diamond, diamond-like carbon, SiC, SiO₂, TiN,cubic boron nitride, silicon nitride, titanium, titanium carbide,cordierite or aluminum nitride; and a plurality of second burs at thesecond side of the main body, wherein the main body is grounded.
 17. Thesubstrate holder of claim 16, wherein the material comprises diamond ordiamond-like carbon.
 18. The substrate holder of claim 16, furthercomprising a layer between the plurality of first burls.
 19. Thesubstrate holder of claim 16, further comprising a heater provided tothe main body and configured to control a temperature of the substrateand/or the main body.
 20. The substrate holder of claim 16, wherein themain body is formed of a different material from the first and/or secondburls.
 21. The substrate holder of claim 16, wherein the number of firstburs distributed across the substrate holder is more than 10,000.
 22. Alithographic apparatus, comprising: a support structure configured tosupport a patterning device; a projection system arranged to project abeam patterned by the patterning device onto a substrate; and asubstrate holder arranged to hold the substrate, the substrate holderbeing according to claim
 16. 23. A substrate holder for use in alithographic apparatus, the substrate holder comprising: a main bodyhaving a first side of the main body and a second side of the main bodyopposite to the first side; a plurality of first burs at the first sideof the main body and having end surfaces to support a substrate; aplurality of second burs at the second side of the main body; and aheater provided to the main body and configured to control a temperatureof the substrate and/or the main body, wherein the main body isgrounded.
 24. The substrate holder of claim 23, further comprising alayer between the plurality of first burls.
 25. The substrate holder ofclaim 23, wherein at least an upper portion of each of the first burlscomprises a material selected from: diamond, diamond-like carbon, SiC,SiO₂, TiN, cubic boron nitride, silicon nitride, titanium, titaniumcarbide, cordierite or aluminum nitride.
 26. The substrate holder ofclaim 23, wherein the main body comprises at least one material selectedfrom: Zerodur ceramic, cordierite, SiSiC, SiC, AlN, SiSiC, ceramic orglass-ceramic.
 27. The substrate holder of claim 23, wherein the mainbody is formed of a different material from the first and/or secondburls.
 28. The substrate holder of claim 23, wherein the number of firstburs distributed across the substrate holder is more than 10,000.
 29. Alithographic apparatus, comprising: a support structure configured tosupport a patterning device; a projection system arranged to project abeam patterned by the patterning device onto a substrate; and asubstrate holder arranged to hold the substrate, the substrate holderbeing according to claim
 23. 30. A substrate holder for use in alithographic apparatus, the substrate holder comprising: a main bodyhaving a first side of the main body and a second side of the main bodyopposite to the first side; a plurality of first burs at the first sideof the main body and having end surfaces to support a substrate; and aplurality of second burs at the second side of the main body, wherein(1) the main body has a thickness in a range of 1 mm to 50 mm, (2) eachof the first burs and/or second burs has a height in a range of about 5μm to about 250 μm, and/or (3) a total area of all the burls on one sideof the main body is less than 3% of the total surface area of the mainbody, and wherein the main body is grounded.
 31. The substrate holder ofclaim 30, further comprising a heater provided to the main body andconfigured to control a temperature of the substrate and/or the mainbody.
 32. The substrate holder of claim 30, wherein the main bodycomprises at least one material selected from: Zerodur ceramic,cordierite, SiSiC, SiC, AlN, SiSiC, ceramic or glass-ceramic.
 33. Thesubstrate holder of claim 30, wherein each of the first burs comprise alower body portion protruding from the main body and an upper bodyportion above the lower body portion, wherein the lower body portionsare a different material than the upper body portions, the upper bodyportions comprise a material selected from: diamond, diamond-likecarbon, SiC, SiO₂, TiN, cubic boron nitride, silicon nitride, titanium,titanium carbide, cordierite or aluminum nitride; and
 34. The substrateholder of claim 30, wherein the number of first burs distributed acrossthe substrate holder is more than 10,000.
 35. A lithographic apparatus,comprising: a support structure configured to support a patterningdevice; a projection system arranged to project a beam patterned by thepatterning device onto a substrate; and a substrate holder arranged tohold the substrate, the substrate holder being according to claim 30.